The present invention relates to an elongate article coating system for paint coating elongate articles, such as wires, pipes,string-like matters or the like and more specifically to a coating thickness regulating device for such a system, for regulating the thickness of the paint applied to the surface of an elongate article.
It has been a common practice to employ, in order to apply paint continuously to the outer surface of an elongate article in a uniform thickness, a process in which the elongate article is immersed and passed through paint contained in a container to coat the elongate article with the paint, and then the coated elongate article is passed through a spreading die, a spreading cloth or felt while the paint is fresh to remove the excessive paint from the elongate article so that the elongate article is coated with a paint film having a comparatively uniform thickness.
However, passing the coated elongate article through a spreading die has the following disadvantages.
First, since an ordinary spreading die is made of a rigid material, such as a metal, and is provided with a spreading hole having a fixed diameter, the variation of the elongate article in diameter causes a variation of the coating in thickness, which results in unsatisfactory coating due to the variation of the drying rate and hardening rate of the coating; secondly, when foreign matters, such as dust, are contained in the paint, the foreign matters scratch the coating to flaw the coating with stripes, or, sometimes, break the elongate article when the elongate article is very slender; thirdly, water paint and oil paint containing an organic solvent tends to collect and harden in the vicinity of the inlet of the spreading die and scratch and flaw the coating; and fourthly, ordinarily, the elongate article is aligned with the spreading die before starting the coating operation in order to form a uniform clearance between the inner circumference of the spreading hole of the spreading die and the outer circumference of the elongate article, however, the elongate article tends to deviate from the correct position and the clearance tends to vary due to the vibration of the elongate article during the coating operation, which provides a paint film having irregular thickness.
Cloth and felt have a flexible and porous structure consisting of natural fibers and/or synthetic fibers each having a low elastic limit and a low abrasion resistance, and hence a spreading cloth or felt is capable of being easily brought into close contact with the surface of the elongate matter. However, a spreading cloth or felt is abraded rapidly causing irregular spreading. Accordingly, a coating thickness regulating device employing cloth or felt as spreading means is unable to operate continuously for an extended period of time under optimum operating conditions.
In order to overcome such disadvantages of a spreading cloth or felt, in a known method, the spreading cloth or felt is impregnated with a suitable amount of paint and packed in a spreading block by applying an appropriate external pressure thereto. However, since cloth and felt have a low elastic limit, the collapse of the voids of the porous structure occurs particularly in the portion near the surface of the running elongate article, and thereby the paint retaining function of the spreading cloth or felt is deteriorated; therefore, it is very difficult to maintain the spreading cloth or felt in an optimum spreading condition and to adjust the packing pressure properly. On the other hand, the abrasion of the portion of the spreading cloth or felt extending around the elongate article increases with increase in the packing pressure. The abraded spreading cloth or felt causes irregular coating and scratches in the paint film. Excessively thick coatings are liable to be dried futilely and, in some cases, are peeled off the elongate article to form uncoated portions in the surface of the elongate article. Uncoated portions are liable to be formed at the start of the coating operation or when the paint is not supplied sufficiently to the immersing process. The uncoated portions increase the friction between the elongate article and the surface of the spreading cloth or felt, which can break the elongate article.